1. Field of the Invention
This invention relates to fire retardant decks for the landing and taking off of helicopters or other vertical takeoff aircraft.
2. Description of the Prior Art
Transportation by helicopter is becoming increasingly important to industry and government. There are large numbers of helicopter landing pads ("helipads") in use throughout the world, not only on land but also on ships and oil drilling rigs. There are over 4000 helipads in the United States alone, of which somewhat less than half are simply circles painted on the ground.
Helipad designers can take many precautionary measures in constructing a helicopter landing pad for maximum safety. The most hazardous portions of helicopter operation are takeoffs and landings. Even if the structural damage to a helicopter is minor in a crash landing on a pad, there is a great risk of fire because of ignition of fuel spilled from the fuel tanks, which are usually located underneath the aircraft. Burning fuel flows onto the landing platform and spreads rapidly to surrounding areas. In such a situation there is an extremely serious danger of harm to personnel and further damage to the helicopter and the landing platform from fire and explosion. What happens immediately after a fuel fire begins determines the ultimate course of the fire and whether the fire may be brought under control.
Active fire-fighting systems for helicopter decks are described in the following patents.
U.S. Pat. No. 4,474,130 (1984) to Birkeland discloses a helicopter deck preferably for use in oil drilling platforms. The periphery of the deck is fitted with a gutter drained by one or more down pipes. Water discharge orifices of a fire extinguishing system are centrally located on the deck. The orifices are supplied with water under pressure for flooding the deck surface, for which control levers are arranged at the periphery of the deck.
U.S. Pat. No. 4,202,646 (1980) to Herstad discloses a helicopter landing platform comprising a fine mesh grid supported on a coarse mesh grid above a horizontal surface such as an ordinary helicopter landing pad. A bottom framework supports the grid structure. Conduits and nozzles for a foam fire extinguishing agent are located in the space between the grid work on top and the framework. Burning fuel flows through the mesh and the foam extinguishes the fire. The mesh prevents the foam from blowing away.
The main disadvantages associated with active fire-fighting systems for helicopter landing pads are complexity, expense, and the need for maintenance to keep them in operational readiness. A helicopter landing deck with an active fire-fighting system is very expensive to construct because the materials are expensive and because the conduits, valves, reservoirs, and other parts form a complicated apparatus to set up. The system must also have regular preventive maintenance to assure that it is always in proper operating order.